The present invention relates in general to a fluid-filtration receptacle, and more particularly, to a fluid-filtration receptacle (such as used in a centrifugal filter unit) provided with a user-variable semi-permeable drain assembly.
Biomoleculesxe2x80x94such as proteins and nucleic acidsxe2x80x94continue to be the subject of intense and broad academic and commercial investigation. Investigation, of course, requires detection. While detection instruments and methodologies continue to evolve in their sophistication, precision, and sensitivity, sample preparation remains important, if not more so. Often, sample contain only minute or trace amounts of a biomolecule being investigated, and accordingly, sample concentration is frequently desired to assure and/or facilitate its detection. Certain detection methodologies also perform better within certain sample volume ranges.
A variety of centrifugal filter units are currently available and continue to be used with good results for sample preparation. Centrifugal filter units commonly comprise a housing to hold the unfiltered sample, a collection tube for the filtered sample, a filter sealed in a manner so that when the sample passes from the housing to the collection tube it must pass through the filter, and a means to collect the concentrated sample from the housing.
Centrifugal filter units are commonly spun in centrifuges using either of two basic types of rotors: i.e., xe2x80x9cswinging bucketxe2x80x9d and xe2x80x9cfixed anglexe2x80x9d. The fixed angle rotor positions the device at a preset angle relative to the axis of rotation or g-force. In the swinging bucket rotor, the device swings out into a position such that the device is or almost parallel to the axis of rotation or g-force. In centrifuges, the maximum forces are generated at the outermost point along the radius of rotation.
To concentrate a component in a liquid sample with a centrifuge device, two features must be present. The membrane or filter must retain the component of interest. This is achieved by having the pores of the membrane smaller than the component so that the component physically can not pass through the membrane. Also, there must be a pocket that is positioned at the outermost point within the housing along the axis of rotation. The pocket must also be positioned relative to the membrane so that liquid in the pocket is not available to flow through the membrane.
In U.S. Pat. No. 4,632,761, issued to W. F. Bowers et al. on Dec. 30, 1986, a device for use in a fixed angle centrifuge rotor is disclosed. The method suggested by Bowers et al. to create a pocket for the concentrate is to either seal the device off or block the downstream side of the membrane by the underdrain structure. The membrane in this device is perpendicular to the centerline of the device. When this device is positioned and spun in a fixed angle centrifuge rotor, the g-force acts at an angle relative to the membrane surface. As the liquid filters through the membrane, a small amount of liquid stops flowing because the g-force pushes the liquid into the pocket. The device side walls of the housing and the outlet holes of the underdrain support structure define this pocket. The volume will change slightly by spinning the device in a rotor with a different fixed angle. Changing the rotor may result is in a more useful concentrate volume, but changing rotors is not a practical approach due to the time and skill required to do so.
In U.S. Pat. No. 4,722,792, issued to T. Miyagi et al. on Feb. 2, 1988, and U.S. Pat. No. 5,647,990, issued to V. Vassarotti on Jul. 15, 1997, there are described centrifuge receptacles wherein a membrane is positioned along one or more of the receptacles"" sidewalls. The membranes are sealed and supported by an underdrain support. When centrifuged, the filtering stops at the membrane seal. More particularly, filtering stops at the highest point in the seal positioned furthest along the axis of rotation. The concentrate volume is preset by the geometry of the pocket formed in the device, and is not intrinsically variable.
The cited patents are representative of the general design of currently-available centrifuge receptacles, i.e., wherein the maximum filtration volume is fixed either by the structure and geometry of the receptacle""s physical configuration and/or the positioning of its installed membrane. Accordingly, to attempt filtration of a volume less than the maximum preset value, the current practicexe2x80x94commonly requiring skilled user intervention during filtrationxe2x80x94is to attempt to stop the filtration process at a time that yields the desired volume. This process can be inconsistent and inaccurate, relies heavily on the experience and skill of the user, and can vary depending on sample viscosity, clogging factors in the sample, membrane characteristics, the starting volume of the sample, and other factors.
When working with a fixed angle centrifuge, two options are available to control the filtration volume. The centrifuging process could be stopped at a time that yields the desired volume. As mentioned, this is unreliable. Alternatively, one could obtain and select among a range of different interchangeable rotors having varying rotor angle. The angle will effect concentration volume, but changing centrifuge rotorsxe2x80x94though possiblexe2x80x94is not a simple matter. It requires time and skill, and thus, may be impractical.
In light of the above, there is a need for a better means for filtering a sample liquid to a variable user-specifiable volume, and particularly, a means that does not require inordinate human intervention and/or oversight once a filtration process on the sample has commenced.
In response to the above needs, the present invention provides a fluid-filtration receptacle capable of filtration, out of the confines of said receptacle, of specifiable volumes of a sample liquid within a predefined volume range. Toward this end, the fluid-filtration receptacle is provided with and characterized by a semi-permeable drain assembly.
More particularly, in respect of its basic structure, the fluid-filtration receptacle comprises a user-fillable liquid-containable internal area, the boundaries of which are defined by an at least partially-enclosing liquid-impermeable solid material (cf., the receptacle walls). The liquid-impermeable solid material having a releasably-sealed semi-permeable drain assembly disposed therethrough. Although subject to variation, in all instances, the semi-permeable drain assembly will be capable of being either completely or variably unsealed by a user to allow draining of a predetermined corresponding volume of a sample liquid from said internal area when the fluid-filtration receptacle is placed in at least one of said predetermined operative positions.
As will be appreciated by those skilled in the art, the fluid-filtration receptacle can find utility in several and various analytical separation methods, and accordingly, will be therein embodied to conform, within the definition of the present invention, with the structural and functional requirements associated therewith. One important method is centrifugation.
In centrifugation, the fluid filtration receptacle will typically be used in combination with a filtrate collection vial, the combination being placed together in a centrifuge holder during a centrifugal operation. Several of the embodiments of the present invention are drawn to applicability within the several classes of centrifuges currently available, the two basic division thereof being so-called xe2x80x9cswinging bucket rotorxe2x80x9d centrifuges and so-called xe2x80x9cfixed angle rotorxe2x80x9d centrifuges. Hence, embodiments are provided herein wherein the semi-permeable drain assembly comprises, for example, several sealed openings each capable of being individually and completely unsealed by a user; or a single sealed semi-permeable opening capable of being variably unsealed by a user; or several discrete openings each comprising a releasable seal and a semi-permeable membrane. Other variations involve the configuration and placement of the drain assembly, the configuration and composition of the seal, and the size and shape of the receptacle.
In light of the above, it is a principal object of the present invention to provide a fluid-filtration receptacle capable of filtering specifiable volumes of a sample liquid.
It is another object of the present invention to provide a fluid-filtration receptacle having integrated therein a releasably-sealed semi-permeable drain assembly that is capable of being either completely or partially unsealed by a user to allow either filtered or selective drainage of a specifiable corresponding volume of the sample liquid.
It is another object of the present invention to provide a fluid-filtration receptacle having integrated therein a releasably-sealed semi-permeable drain assembly, the fluid-filtration receptacle being comparatively easy to manufacture and comparatively easy to use.
It is another object of the present invention to provide a centrifugal filter unit capable of concentrating a sample liquid by removing by filtration in a centrifuge specific volumes of liquid from said sample, the concentration being accomplished without critical reliance on the duration of the centrifugal operation.
It is another object of the present invention to provide a centrifugal filter unit comprising (pre-assembled or in a kit) a fluid filtration receptacle and a filtrate collection vial, the fluid-filtration receptacle being (or capable of being) snugly xe2x80x9cnestedxe2x80x9d in the filtrate collection vial.